Various forms of controls for the power supply to an A.C. load are known which controls will increase or reduce the power to the load. Thus, for example, a rheostat connected in series with an electric light bulb can be adjusted to increase or decrease the power at the light bulb and thereby change the degree of illumination therefrom. A silicon controlled rectifier (SCR) or a triac is connected in series with a load, with a firing angle control being connected to the SCR, to adjust the amount of each alternating current pulse received by the load and thus control the amount of A.C. power that the load receives. In the main, such prior art devices require a manual manipulation in order to achieve the desired result.
Proximity controls are known wherein a person's resistance or capacitance is applied to an electronic circuit to produce an output signal, which output signal is then used to effect a desired result. In the main, the output signals of proximity detectors have been merely on-off signals, as distinguished from a proportional control wherein the signal has a magnitude which is a function of the length of time that the person's capacitance or resistance is applied to the detector. However, U.S. Pat. No. 3,736,445 discloses a proximity detector which operates an SCR to adjust the power to a load in accordance with the length of time that a person's body is present to effect an electrical coupling in the proximity detector circuit; that is, it is a proportional control operated by a proximity detector. The device of this patent employs an oscillator component which is connected to a touch plate and two sensors connected to respective touch plates. When a person contacts the oscillator touch plate and one of the sensor touch plates his body completes a circuit between the oscillator and the respective sensor (much as would the connection of a wire or the closing of a switch therebetween) so as to actuate the sensor. As compared to such a prior art device, the present invention greatly simplifies the proximity control by reason of the fact that it does not employ an oscillator component (as that term is conventionally used). Instead, it employs the standard alternating current source, used to power the unit, as the oscillator. The elimination of the oscillator component significantly reduces the cost of the apparatus and also reduces the overall apparatus size. This broadens the range of application of such a control. Thereby, for example, it can be embodied in an ordinary house light or lamp or it can be mounted in a switchbox. Furthermore, it is not necessary that two touch plates or the like be employed which must be contacted simultaneously in order to connect the oscillator to the sensor. A single touch plate for each sensor is all that need be contacted by the individual in order to actuate the control in a given sense of change.
Like the proportional control referred to, the present invention employs a capacitor connected in parallel with an amplifier as a memory in order to maintain an established operational level when a person's body is not being sensed. However, in the present invention the resistance in the capacitor circuit is very high, i.e., at least ten million megohms, so as to prevent any significant leakage of the charge on the capacitor. Thus, with embodiments of the present invention, the unit can be unplugged from the A.C. power source for a period of even days and when it is plugged back in, the power supply to the load will correspond to the level established at the time the unit was unplugged because the charge on the memory capacitor is substantially unchanged.
A further important distinction of the present invention lies in the simplicity of a sensor. Each of the two sensors is a unipolar current pump. Essentially each comprises nothing more than a diode and a voltage sensitive switch. The diode of one sensor is arranged so that current is pumped only in one direction with respect to the memory capacitor and the diode of the other sensor permits current to be pumped only in the opposite direction when a person's capacitance is applied to the sensor. Each diode is connected to the memory capacitor by a respective voltage sensitive switch. While various forms of voltage sensitive switches could be utilized, a neon bulb represents the ultimate in simplicity. It has the further advantage that is presents a high resistance against leakage of a charge on the memory capacitor when it is in the dormant state. When the current pump of one sensor is activated by a person's capacitance being applied thereacross, a voltage is reached which is sufficiently high to cause the neon bulb to fire resulting in current being applied across the memory capacitor to add to, or substract from, as the case may be, the charge on the memory capacitor. This occurs during a portion of each cycle and as soon as the voltage across the neon bulb drops below the level required to maintain conduction in the neon bulb, the current flow ceases. The number of cycles during which such pumping action occurs is determined by the length of time that a person's capacitance is applied to the sensor.
Another feature of the present invention is the floating ground reference of the apparatus, as distinguished from the earth ground (which is the ground to which one of the power supply wires is connected). This permits, for example, the apparatus to be plugged into a wall socket in either orientation of the plug with respect to the socket, without changing the manner in which the apparatus operates. The apparatus disclosed in U.S. Pat. No. 3,641,410 includes a current pump which operates through a neon bulb as a switch. However, with that apparatus, it is necessary, in order not to change the function of the apparatus, to have the plug inserted into the wall socket with a predetermined orientation. With a proximity control such as might be used on a table lamp, for example, it is undesirable to require that the plug be inserted into the socket in a particular orientation in order to maintain the proper ground connection. Many users of table lamps have outlets which are not polarized and therefore such a requirement would limit the saleability of the lamp. Furthermore, a possibility that the outlet has been incorrectly connected always exists and an incorrect connection could change the orientation with respect to earth ground.
Another feature of the invention is that a limit control is incorporated to establish the maximum charge that may be placed upon the memory capacitor. Without such a control, it is possible for the charge on the memory capacitor to be increased substantially beyond the range within which the power applied to the load is at a maximum. When this occurs, there is a substantial lag in diminishing the power supply to the load because, before any change in the power to the load can be effected, the voltage on the memory capacitor must be brought back within the operating range. The time lag thereby occasioned is eliminated by the limit control on the maximum charge of the memory capacitor. In the disclosed embodiment of this limit control, it incorporates a transistor which also doubles as the diode for the increase current pump.